1. Field of the Invention
The present invention relates to a test circuit, and more particularly, to a test circuit for checking whether at least one programmable gain amplifier (PGA) operates correctly.
2. Description of the Prior Art
In conventional practice, an extra test device is required for checking a mixed signal integrated circuit (IC). FIG. 1 is a diagram illustrating a conventional test device for an audio codec 10. To determine whether the audio codec 10 operates correctly, the conventional test method utilizes an analog to digital converter (ADC) and a digital signal processor (DSP), both of which are external to the audio codec 10. First, the ADC converts an analog output of the audio codec 10 into digital information. Then, the DSP performs a calculation on a plurality of digital information to get an average value. The average value is compared with a predetermined value to determine whether the audio codec 10 operates correctly.
To make the test result more reliable, it is necessary to lengthen the test time. However, the test efficiency decreases proportionally as the test time gets longer.